SOHC.co.uk Forums > CB350/400

Carbs overflow

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AndyD:
Oddjob,
Interesting test - I've tried almost everything else with my carbs and they still leak like a sieve as soon as petrol is turned on.
As they're back on the bench I gave your idea a go and the pressure drops steadily with 'dry' float needles but as soon as I spray a little WD40 over them they seal and hold pressure.
This is with new DSS float valves fitted - tomorrow I'll put the old ones back in and see if they are any different.
What I can't understand is that the flow is so strong when the fuel is turned on that it seems hard to believe it's just leakage past the needle.
I did wonder if there was maybe something that held the floats down and I'll have a good look at this possibility as well.
Also when trawling t'interweb there are some comments on setting fuel height rather than float height and I wondered if this was an option on the 400. Certainly on the GS and GSX I've got that is the way they are set, using clear tubes from the drain plug. I did see some comments saying this could be done on the 400, set at around 3-4mm below the float bowl joint.
The saga continues
Cheers,
Andy

AndyD:
Had another play with the carbs on the bench today and tried the original valve seats / needles but these let pressure drop significantly quicker than the Keyster ones despite repeated cleaning and polishing etc.
One thing I did notice was that without the bottom bowl, the floats could occasionally stick open when turned over and then drop down with any movement. Nothing seems to be rubbing or catching and I think the spring thingy in the bottom bowl would also limit how far the floats can drop when fitted.
I plugged in the float height gauges I made up for the GS1000 a while ago to see if this could shed any light on the problem and they certainly help see what's happening.
Sure enough as soon as fuel is turned on the carbs fill and then overflow at a quick rate.
Turned the fuel off, gave the whole assembly a good shake and when turned back on the fuel level stayed at the right level.
Left them for an hour or so and no leaks.
Drained them and then turned fuel on and once again the levels go too high and overflow. And again, turning off the fuel and shaking them stops the leaking.
So it looks like for some reason the floats on initial filling don't shut off the supply but once they are 'encouraged' with a shake they work fine.
Floats and pins etc. all look fine and move very easily so I can't see any reason for this behaviour so may play a bit more on the bench before wrestling with the airbox etc. to put on the bike again.
Cheers,
Andy

Bryanj:
Slightest bid of crud or roughness on the pivot pin or iside the pivot tube can cause all sorts of troubles

AndyD:
Thanks Bryan,
I'll pop the bowls off one last time and give the pivots a final check / clean then I think I'll try them on the bike and keep fingers crossed.

Cheers,
Andy

DaveN:
Does anyone know if you can buy replacement pivot pins?

One of mine has been mangled and is shorter than the others.

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